.topnav {
  overflow: hidden;
  background-color: #333;
}

.topnav a {
  float: left;
  color: #f2f2f2;
  text-align: center;
  padding: 16px 24px;
  font-size: 17px;
  text-decoration: none;
  display: block;
}

.topnav a:hover {
  background-color: #ddd;
  color: black;
}

.topnav a.active {
  background-color: #ff1a1a;
  color: white;
}
    
div, article {
    padding: 16px;
    background-color: lightgrey;
}    

footer {
    padding:16px;
    background-color:  #ff1a1a;
}

.summary {
    padding-left: 36px;
}

details > p {
    padding-left: 36px;
}

details > summary {
    font-size: 24px;
}

details li {
    color: red;
}